The present invention relates to a low-pressure TEOS process, more specifically, to a low-pressure TEOS process inducing few particles.
Dielectric materials, such as oxide, nitride, oxynitride, phosphosilicate glass (PSG) and borophosphosilicate glass (BPSG), play a significant role in the field of semiconductor industry. All of the dielectric materials contain silicon and are generally deposited by performing atmospheric chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), or plasma enhanced chemical vapor deposition (PECVD). There are two kinds of reactive gases for forming a dielectric film containing silicon in semiconductor industry, e.g. silane-based (silane) gases and TEOS-based (Tetra-Ethyl-Ortho-Silicate) gases.
TEOS is an organic silicate containing silicon and oxygen, and it is in liquid phase under room temperature and atmospheric pressure. During a deposition process, the TEOS liquid is heated to a temperature between 40 to 70xc2x0 C. in order to increase its saturation vapor pressure. In the meanwhile, the semiconductor substrate needs to be heated to a temperature between 700 to 750xc2x0 C. under low pressure (about 0.5 torr). The low-pressure TEOS process is widely applied in the semiconductor industry because of its good step coverage, such as the process for forming dielectric sidewall spacer.
The low-pressure TEOS process is generally performed in a reactor of tubular type. The reactor is composed of annealed quartz, containing a heater surrounding its outer sidewall for heating. During a deposition process, a lot of semiconductor substrates standing side by side in a boat are transferred into the reactor. Please refer first to FIG. 1, which shows a schematic diagram of a boat. The boat 20 has lots of flanges 30 in its internal sidewall, each of which can carry one semiconductor substrate 10. After the deposition process is accomplished, the substrates are transferred out of the reactor together with the boat.
However, according to the prior art, a plenty of particles 40 are generally produced on the semiconductor substrate 10 around the regions in contact with the corners of the flange after the deposition process, as shown in FIG. 2. From EDS (Energy Dispersive Spectroscopy) data, the particles 40 are affirmed to be composed of silicon oxide. For this reason, we can conclude that the particle contamination results from the low-pressure TEOS process. During the deposition process, the silicon oxide films are deposited not only on the semiconductor substrates, but also on the flanges of the boat. Because the corners of the flanges have much larger geometric curvature, the oxide films deposited on the corners of the flanges have larger stress, which results in poorer adhesion. The poor adhesion will frequently induce particles falling on the surface of the substrates.
According to the prior art, the boat should be changed and cleaned after a several of runs to prevent particle contamination. Therefore, not only the production throughput decreases, but also the loading of maintenance engineers largely increases in accordance with the prior art.
Accordingly, it is a primary object of the present invention to provide a few-particle-induced low-pressure TEOS process.
It is another object of the present invention to provide a method of enhancing the throughput of a low-pressure TEOS process.
A few-particle-induced low-pressure TEOS process is disclosed. First, a lot of semiconductor substrates are arranged on a boat and transferred into a TEOS reactor. Silicon oxide films are then deposited on the semiconductor substrates by performing a conventional low-pressure TEOS process. Before the substrates are sent out of the reactor, an annealing process is performed by injecting oxygen gas into the reactor to solidify the oxide films on the corners of the boat""s flanges. The annealing process is performed under a pressure between 0.3 torr to 0.7 torr for a duration between 10 minutes to 50 minutes, and the substrates keep being heated to a temperature between 700 to 750xc2x0 C. during the annealing process.
Another few-particle-induced low-pressure TEOS process is disclosed in another embodiment. First, a lot of semiconductor substrates are arranged on a boat and transferred into a TEOS reactor. Silicon oxide films are then deposited on the semiconductor substrates by performing a conventional low-pressure TEOS process. Before the substrates are sent out of the reactor, an annealing process is performed by injecting oxygen gas into the reactor to solidify the oxide films on the corners of the boat""s flanges. After sending the boat out of said reactor, a next lot of semiconductor substrates are arranged on the boat and then transferred into the TEOS reactor. Thereafter, the steps mentioned above are repeated for 5 to 15 times to accomplish the low-pressure TEOS process for 5 to 15 lots of semiconductor substrates. After that, the boat is sent into the reactor without carrying semiconductor substrates. Finally, a strengthening annealing process is performed by injecting oxygen gas into the reactor to solidify the oxide films on the corners of the boat""s flanges.